The present invention relates to apparatus for measuring the aerodynamic pressure distribution acting on the surface of the spinning wind tunnel model.
The so-called "Magnus effect" refers to the aerodynamic forces and moments acting on a spinning body whose flight direction is not aligned with its axis of spin. The Magnus phenomena are of particular importance in the ordnance field. In the case of spin stabilized projectiles, for example, the combination of projectile spin and angle of attack results in a Magnus force and moment which often degrade their flight performance. Although the Magnus effects are small as compared to the non-spinning static aerodynamic forces and moments, they often have a significant influence on the projectile stability and consequent flight motion and trajectory. The Magnus effect has been cited as the cause of the poor performance and failures of several projectile-based weapon systems.
The Magnus phenomena have been extensively investigated by both theoretical and experimental means as noted by I. D. Jacobson in AGARDograph, No. 171, November, 1973. However, quantitative experimental data have been limited to force and moment type measurements either obtained directly from wind tunnels or indirectly from ballistic ranges. While providing useful information with regard to the projectile flight stability and trajectory, they often do not give a detailed insight into the cause of the resulting forces and moments.
Additional knowledge concerning the Magnus effect could be gained by the experimental determination of the surface pressures acting on spinning bodies. If such data were available, it might provide a better understanding of the Magnus phenomena and would be an invaluable aid toward evolving a theoretical fluid dynamic model.
Experimental determination of the pressure distribution acting on the surface of a wind tunnel model is a basic and vital step in the design and analysis of aircraft, missiles, and other aerodynamic devices. Yet, up to now, these tests have always been limited to non-spinning conditions. The complete pressure distribution acting on the surface of a spinning body has never been experimentally obtained, even for the most simple cases.
Pressure measurements near the surface of spinning bodies can be obtained by simple static and total head pressure probes. However, their alignment with the local air flow direction and their proximity to the body surface is critical. Also, the body surface must not contain any protuberance which could physically interfere with the probes. In addition, the probe itself can create local flow disturbances which could effect the validity of the measured data. Thus there exists a need for instrumentation which can accurately measure the surface pressure on a spinning aerodynamic body without interfering with or disturbing the aerodynamic flow near the body.